The inheritance and development of cup and disc diameters.

The familial resemblances in discs diameter (d) and cup diameter residual (e) were studied in 845 individuals forming 297 families and 1040 pairs of spouses and first-degree relatives. The cup diameter residual was computed as the difference between the observed cup diameter and the cup diameter expected from the disc diameter and the age, according to a multiple regression equation. The results for d and e were similar. Spouses did not resemble each other at all. The resemblance between first-degree relatives, on the other hand, was quite substantial. There were no major influences of sex-linkage, dominance or common environment and no obvious maternal effects. It was concluded that the familial resemblance was essentially additively genetic in origin. The heritability was estimated at 2/3. The remaining variance was attributed to errors of development. The results can be applied to other surface dimensions of the optic nerve head.